1. Field of the Invention
The present invention relates to an image blur correction apparatus for correcting an image blur produced by hand vibrations and the like in a camera, optical equipment, and the like.
2. Related Background Art
Since all operations such as exposure determination, focusing, and the like important for photographing are automated in contemporary cameras, even a person who is not skilled in camera operation rarely fails in taking pictures.
In recent years, a system for correcting an image blur produced by hand vibrations acting on a camera has been studied, and nearly all factors that lead to photographing failures are removed.
A system for correcting an image blur produced by hand vibrations will be briefly explained below.
Hand vibrations of a camera upon photographing normally have a frequency ranging from 1 Hz to 12 Hz. In order to take a picture free from any image blur even when such hand vibrations have been produced upon releasing the shutter, simply stated, vibrations of the camera produced by hand vibrations must be detected, and a correction lens must be displaced according to the detection value. Hence, in order to take a picture free from any image blur even when hand vibrations have been produced, camera vibrations must be accurately detected as a first requirement, and changes in optical axis arising from the camera vibrations must be corrected by displacing the correction lens as a second requirement.
In principle, such vibrations (camera vibrations) can be detected by mounting, in a camera, a vibration detection device or the like, which is comprised of a vibration detection portion for detecting acceleration, velocity, or the like, an integrator for electrically or mechanically integrating the output signal from the vibration detection portion to output a displacement, and the like. An internal correction optical device is controlled to change the photographing optical axis based on the detection information or the like, i.e., a correction optical system is displaced via a driving means to attain image blur correction.
In order to drive the correction optical system, a coil and magnet are conventionally used as a driving means. The coil or magnet is set on a stationary portion, the magnet or coil is set in the correction optical system, and the optical system is driven by supplying a current to the coil. In an image blur correction device proposed, when the vibration detection device detects vibrations in a vertical vibration direction (to be referred to as a pitch direction hereinafter) upon holding the camera at normal position, and in a horizontal direction (to be referred to as a yaw direction hereinafter) perpendicular to the pitch direction, the driving means (two sets of driving means are set to correct vibrations in the two directions, i.e., the pitch and yaw directions) are independently driven in the two directions.
With the above-mentioned image blur correction device, the photographer can enjoy less strict photographing conditions regardless of hand vibrations, but since the driving means for driving the correction optical system are added, the following problems are feared.
First, when the photographer inadvertently moves the camera before actual photographing, a large vibration amount is detected, and an unnecessarily large current is supplied to the driving means for the correction optical system. As a consequence, the camera battery is wasted, thus disturbing energy and power savings.
Second, when a large current is supplied to drive the correction optical system while film feeding or electronic flash charging is in progress, large current loads are superposed, thus posing a serious problem in the camera system.
To solve such problems, a current restricting means for restricting the current to be supplied to the driving means for the correction optical system is used to attain power savings in the driving means.
However, when the correction optical system is driven in the two directions, i.e., pitch and yaw directions, the loads acting on the driving means in the individual directions are not always equal to each other as they largely depend on gravitation acting on the correction optical system. More specifically, since an extra load acts in driving the correction optical system in the gravitation direction, a larger load acts on the driving means in the gravitation direction. However, conventionally, since the current restricting levels that allow currents to be supplied to the driving means for the correction optical system assume equal values in both the pitch and yaw direction regardless of any imbalance corresponding to the weight of the correction optical system, the driving force of the driving means in the gravitation direction considerably deteriorates as compared to the driving means in the other direction.